I'm running a homebrew turnstile antenna, with a reflector, that is fed with about 45 feet of low-loss RG-8 coax. The coax is feeding the latest version of the Funcube Dongle. I'm wondering if a pre-amp would help me receive more of the telemetry data then I get now, particularly on the low passes. I'd appreciate any thoughts on this.

The simple answer is, yes. Especially if you mount the preamp at the antenna to help overcome the loss and injected noise of the coax. There are many who will take the opposite position that a preamp is not required. However, from my experience, a preamp is very, very helpful.

Think of the pre-amp as making up for the losses in the feed-line.Look up the attenuation for RG-8 coax at 145MHzIf you are not hearing the satellite near the horizon you may needto improve your antenna. I'm using a home-brew eggbeater with AMSAT preampat the antenna.I start decoding from 6 degrees above the horizon.I'm looking to improve on that with a home-brew QFH (Google it) antenna.The Turnstyle is really just a basic antenna to get you started.